1. Technical Field
The present invention relates to field emission devices, and particularly to a field emission device using carbon nanotube yarns as emitters and method for making the field emission device.
2. Discussion of Related Art
Field emission materials are used in a variety of application such as flat panel displays to emit electrons. Typical field emission materials include, for example, molybdenum (Mo), tantalum (Ta), silicon (Si), and diamond. However, such materials need high emission voltages to emit electrons, and cannot carry high electric current reliably. Carbon nanotubes typically have superior performance including, in particular, good electron emission capability at low emission voltages, generally less than 100 volts. Furthermore, carbon nanotubes can carry high electric current reliably Due to these properties, carbon nanotubes are considered to be an ideal field emission material for a variety of applications, especially in field emission displays.
Carbon nanotube-based field emission devices typically include a base acting as a cathode plate, and a carbon nanotube array acting as an emitter formed on the base. Methods for forming the carbon nanotube array on the base typically include mechanical means and in situ growth. The mechanical means consists of fixing carbon nanotubes onto the base with chemical agglutinant using a robot arm. Such a mechanical means is time consuming and difficult to operate. Furthermore, it is impossible to manipulate the carbon nanotubes with a diameter smaller than about 1 nm (nanometer).
The in situ growth process is generally performed as follows. Firstly, a catalyst film is deposited on a base. The base has a driving circuit preformed thereon. Secondly, a carbon nanotube array is grown on the base by a chemical vapor deposition (CVD) process. However, the carbon nanotube array is generally fabricated under a temperature in the range from 500 to 900° C. As a result, the driving circuit on the base may be damaged.